Problem: If $x \circledcirc y = x-5y$ and $x \triangleleft y = 7x+y$, find $4 \triangleleft (0 \circledcirc 5)$.
First, find $0 \circledcirc 5$ $ 0 \circledcirc 5 = 0-(5)(5)$ $ \hphantom{0 \circledcirc 5} = -25$ Now, find $4 \triangleleft -25$ $ 4 \triangleleft -25 = (7)(4)-25$ $ \hphantom{4 \triangleleft -25} = 3$.